1. Field
An aspect of the embodiments discussed herein is directed to a semiconductor device having a multilayer wiring structure and a method of manufacturing such a semiconductor device.
2. Description of the Related Art
Semiconductor integrated circuits manufactured today each contain vast numbers of semiconductor elements on the common board thereof and employ a multilayer wiring structure to connect such semiconductor elements with each other.
In a multilayer wiring structure, interlayer insulating films, in each of which wiring patterns are embedded to form a wiring layer, are laminated, and via contacts formed inside the interlayer insulating films connect the upper wiring layer and the lower wiring layer.
In particular, in current ultrafine and ultrahigh-speed semiconductor devices, low-dielectric-constant films (so-called low-k films) are used as such interlayer insulating films to reduce the problem of signal delay, for example RC delay, that occurs in a multilayer wiring structure, as well as low-resistance copper (Cu) patterns used as wiring patterns.
In this type of multilayer wiring structure, in which Cu wiring patterns are embedded in interlayer insulating films with a low dielectric constant, it is desirable to pattern the Cu layer by dry etching. A method often used to pattern the Cu layer by dry etching is a so-called damascene or dual damascene process, wherein wiring trenches or via holes are carved through interlayer insulating films in advance. These wiring trenches or via holes are filled with a Cu layer and then unnecessary portions of the Cu layer remaining on the interlayer insulating films are removed by chemical mechanical polishing (CMP).
Any direct contact of a Cu wiring pattern with an interlayer insulating film in this process would cause Cu atoms to diffuse into the interlayer insulating film, thereby leading to short circuits or other defects. These short circuits or other defects are generally avoided by covering the side walls and bottoms of wiring trenches or via holes used to form Cu wiring patterns with conductive diffusion barriers, also known as barrier metal films, and then coating the barrier metal films with a Cu layer. Examples of materials used for such a barrier metal film may include a high-melting-point metal such as tantalum (Ta), titanium (Ti), and tungsten (W) as well as conductive nitrides thereof.
However, in ultrafine and ultrahigh-speed semiconductor device based on current 45-nm technology or newer technologies, the size of wiring trenches or via holes carved through interlayer insulating films is significantly reduced along with miniaturization. To achieve desirable reduction in the resistance of wiring while using such a high-dielectric-constant barrier metal film, it is accordingly necessary that each of barrier metal films covering such ultrafine wiring trenches or via holes is as thin as possible while seamlessly covering the side walls and bottoms of the wiring trenches or via holes.
A technique that has been proposed to address this situation is direct covering of wiring trenches or via holes carved through interlayer insulating films with a copper-manganese alloy layer (Cu—Mn alloy layer). In this technique, Mn atoms contained in a Cu—Mn alloy layer react with Si and oxygen atoms contained in an interlayer insulating film and thus a manganese-silicon oxide layer having a thickness in the range of 2 nm to 3 nm and a composition of MnSixOy is formed inside the Cu—Mn alloy layer as a diffusion barrier film.
However, it is known that in this technique the internally formed manganese-silicon oxide layer contains manganese (Mn) at a too low concentration and thus the adhesion of that layer to a Cu film is problematically weak.
Consequently, another structure of a barrier metal film in which a Cu—Mn alloy layer is combined with a barrier metal film based on a high-melting-point metal such as Ta or Ti has been proposed.
Such a barrier metal structure combining a Cu—Mn alloy layer with a barrier metal film based on a high-melting-point metal such as Ta or Ti provides preferable characteristics with improved resistance to oxidation through the sequence described below.
Recently, use of low-dielectric-constant porous films as a low-dielectric-constant material constituting interlayer insulating films has been proposed to prevent signal delay, for example RC delay. However, unfortunately, such a low-dielectric-constant porous material has a low density and thus is likely to be damaged by plasma during the manufacturing process, and a damaged film often retains moisture on the surface and inside thereof. Accordingly, a barrier metal film formed on such a low-dielectric-constant porous film would be likely to be oxidized by moisture retained inside and this often results in deteriorated characteristics of the barrier metal film and poor adhesion thereof to a Cu wiring layer or a via plug.
On the other hand, the Cu—Mn alloy layer described above contains Mn atoms, and if the layer is used as a seed layer, these Mn atoms react with oxidized portions of a barrier metal film, thereby ensuring characteristics of the barrier metal film necessary for its use as a diffusion barrier and maintaining high adhesion thereof to a Cu wiring layer or a via plug.
Related information may be found in the following patent documents:
Patent Document 1: Japanese Laid-open Patent Publication No. 2007-142236;
Patent Document 2: Japanese Laid-open Patent Publication No. 2005-277390.